Nonfogging transparent material

ABSTRACT

A transparent nonfogging coating is applied to a normally fogging transparent or reflecting substrate. The nonfogging coating preferably comprises a hydrophilic acrylate or methacrylate polymer. The polymer can be modified by copolymerization with a monobasic or polybasic unsaturated carboxylic acid or partial ester thereof. The polymer can be cross-linked with a polyepoxide to increase its hardness. Typical substrates include automobile, train and airplane windows, sunglasses, camera lens, microscope lens, binocular lens, telescope lens, meat wrappers, diving masks, ski glasses, mirrors.

United States Patent Shepherd et a1.

[ 1 Jan. 18, 1972 [54] NONFOGGING TRANSPARENT MATERIAL [72] Inventors: Thomas H. Shepherd, Hopewell; Francis E. Gould, Princeton, both of NJ.

[73] Assignee: National Patent Development Corporation,

New York, NY.

[22] Filed: July 28, 1969 [21] Appl. No.: 845,283

Related US. Application Data [60] Division of Ser. No. 738,887, June 21, 1968, Pat. No. 3,448,215, which is a continuation-in-part of Ser. No. 567,856, July 26, 1966, Pat. No. 3,520,949, and a continuation-in-part of 650,259, June 30, 1967, abandoned, and a continuation-in-part of 654,044, July 5, 1967.

[52] U.S.Cl. ..117/124 D,l17/16l UN [51] lnt.Cl ..C03c 17/28 [58] Field ofSearch ...1 17/124 D, 161UC, 161 UN;

[56] References Cited UNITED STATES PATENTS 3,488,215 1/1970 Shepherd etal. ..117/124 3,079,434 2/1963 Christenson et al ..1 17/124 D X 3,267,174 8/1966 Fry et al. ..1 17/161 UC 3,414,635 12/1968 Edwards et all... .117/161 UC X 3,459,698 8/1969 Mantell et al. ..1 17/161 UC 3,464,938 9/1969 Nordstrom ..1 17/124 D X FOREIGN PATENTS OR APPLICATIONS 848,873 9/1960 Great Britain ..1 17/124 Primary Examiner-Alfred L. Leavitt Assistant Examiner-Wayne F. Cyron Attorney-Cushman, Darby & Cushman [57] ABSTRACT Typical substrates include automobile, train and airplane windows, sunglasses, camera lens, microscope lens, binocular lens, telescope lens, meat wrappers, diving masks, ski glasses, mirrors.

6 Claims, 6 Drawing Figures PATENTED JAN} 8 1972 INVENTORS ATTORNEYS NUNFOGGHNG TRANSPARENT MATERML This application is a division of application Ser. No. 738,887, filed June 21, 1968, now US. Pat. No. 3,488,215, which is a continuation-impart of application Ser, No. 567,856, filed July 26, 1966, now US. Pat. No. 3,520,949; application Ser. No. 650,259, filed June 30, 1967, now abandoned; and application Ser. No. 654,044, filed .lluly 5, 1967."

The present invention relates to a nonfogging coating for transparent or reflecting substrates normally subject to fogging.

The problem of fogging of automobile, train and airplane windows as well as lens such as eyeglasses, binoculars, camera lenses, mirror and other transparent or reflecting surfaces made of glass, plastic or metal is well known. At present no effective means have been developed to overcome these problems. The situation is particularly serious in connection with automobiles where the fogging of the windshield or backlight makes driving exceedingly hazardous.

Accordingly, it is an object of the present invention to develop a transparent, nonfogging coating for transparent or reflecting surfaces.

A more specific object is to for automobile windows.

Another object is to develop a transparent, scratch, solvent and abrasion resistant coating for transparent or reflecting surfaces made of glass, plastic or metal.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

It has now been found that these objects can be attained by employing as a coating for a transparent or reflecting surface a coating of a hydrophilic polymer, preferably a hydrophilic acrylate or methacrylate. The hydrophilic acrylate or methacrylate, for example, absorbs water and makes the surface clear under conditions which normally cause fogging of the transparent surface. When large amounts of water are absorbed the polymers have a tendency to be soft and gummy. It has been found desirable for best results to copolymen'ze 80 to 99 percent, usually 85 to 98 percent, of the acrylate or methacrylate with 20 to 1 percent, usually 2 to percent, of an ethylenically unsaturated mono or polycarboxylic acid or partial ester of an ethylenically unsaturated polycarboxylic acid.

The hydrophilic monomer is preferably a hydroxyalkyl mono acrylate or methacrylate such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, diethylene glycol monoacrylate, diethylene glycol monomethacrylate, hydroxy propyl acrylates and methacrylates, e.g., Z-hydroxypropyl acrylate, 2hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, dipropylene glycol monomethacrylate. Acrylamide, methylol acrylamide, methacrylamide and methylol methacrylamide also are useful hydrophilic monomers as is diacetone acrylamide.

In preparing hydroxyalkyl monoacrylates and methacrylates a small amount of the diacrylate or dimethacrylate is also formed. This need not be removed and in fact its presence is frequently helpful in forming, hard, abrasion, scratch and solvent resistant coatings. Usually not over 2 percent of such monomer, e.g., ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate or the like, is employed.

As the ethylenically unsaturated acid there can be used acrylic acid, cinnamic acid, crotonic acid, methacrylic acid, itaconic acid, aconitic acid, maleic acid, fumaric acid, measaconic acid and citraconic acid. Also, there can be used partial esters such as mono 2-hydroxypropyl itaconate, mono 2-hydroxyethyl itaconate, mono 2-hydroxyethyl citraconate, mono 2-hydroxypropyl aconitate, mono 2'hydroxyethyl prepare a transparent coating maleate, mono 2-hydroxypropyl fumarate, mono methyl itaconate, monoethyl itaconate, mono Methyl Cellosolve ester of itaconic acid (Methyl Cellosolve is the monomethyl ether of diethylene glycol), mono Methyl Cellosolve ester of maleic acid.

The hydrophilic polymers and especially the copolymers used in the present invention impart transparent, scratch, solvent and abrasion resistant, nonfogging coatings to glass, metal and plastic transparent reflecting surfaces.

A fogging eifect usually results from the condensation of a portion of the moisture content of warm air on a cool surface.

The transparent reflecting surfaces which can be treated include glass surfaces such as automobile windows, e.g., the windshield, backlight and side windows, train windows, windows in buildings, e.g., apartments, homes, stores and office buildings, glass mirrors, eyeglasses including for example conventional eyeglasses, sunglasses, diving masks and ski glasses, camera lenses, microscope lenses, telescope lenses, binoculars and opera glasses, gunsights, drinking glasses (whereby the condensation occurring when iced drinks are placed therein is eliminated), transparent plastic surfaces including airplane windows, car and train windows, transparent films and containers used as coverings for packaged foods, e.g., meat packaged in a tray having a transparent top film of biaxially oriented irradiated polyethylene, reflecting metal surfaces such as chrome mirrors, etc.

As used in the present specification and claims the term automobile is intended to cover cars, trucks, buses and all other automotive vehicles.

The transparent plastic having a fogging tendency can be polymerized methyl methacrylate, polycarbonate, e.g., 4,4- isopropylidene diphenol polycarbonate as well as other polycarbonates as shown in Fritz Pat. No. 3,305,520 and Christopher and Fox Polycarbonates (pages 161-176 (1962), diethylene glycol bis (allyl carbonate) cellulose acetate, cellulose propionate, cellulose acetate-propionate, biaxially oriented polyethylene, biaxially oriented irradiated polyethylene (e.g., irradiated to 2-20 megarad), biaxially oriented polypropylene, biaxially oriented polystyrene, biaxially oriented styrene-acrylonitrile copolymer, biaxially oriented polyethylene terephthalate (Mylar), biaxially oriented vinyl chloride, biaxially oriented vinylidene chloride polymers, e.g., vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, quench-chilled polyethylene, quench-chilled polypropylene and transparent fogging plastics made by other conventional techniques.

As stated reflecting metal surfaces can be made nonfogging as can reflecting plastic, e.g., metallized mylar or reflecting glass, e.g., a mirror (glass having a metal backing).

Glass windows, for example, can be in the form of tempered glass, plate glass or safety glass, e.g., two layers of glass laminated together with a thin layer of polyvinyl butyral or two layers of glass bonded together with Volan (methacrylate chromic chloride).

The hydrophilic polymer nonfog coating is preferably applied to the transparent or reflecting substrate as a film of l-3 mils thickness. Films as low as 0.25 mil can be employed but there is a greater tendency for fogging to occur. There is no maximum thickness for the nonfog coating, e.g., films of 10 mils or more can be applied, but no further advantages are ob tained to justify the increased cost of the nonfog coating.

The nonfog coating can be applied to the transparent or reflecting surface by spraying from a solution or dispersion of the polymer followed by curing of the polymer which can be hastened, e.g., with heat or catalyst. The hydrophilic monomer for example can be percent converted before being applied to the surface, e.g., glass, and then cured. Advantageously a small amount, e.g., O. l0.2 percent of catalyst such as a peroxide is added to hasten the cure.

it" the hydrophilic monomer containing the unsaturated carboxylic acid modifier is percent converted to the copolymer then monomers of the hydroxyalkyl methacrylate or the like and itaconic acid or the like can be added to give a mixture containing 80 percent copolymer and percent monomer for example and this mixture flowed or sprayed on the transparent surface or the transparent surface can be dipped in the mixture and the hydrophilic copolymer cured. The amount of monomers added back can be from I to percent.

To the already formed polymer before applying it to glass there can be added any conventional cross-linking agent in an amount of 0.25 to 20 percent, preferably 0.5 to 10 percent, most preferably to 8-l 1 percent. The cross-linking agent should be one which does not interfere with the transparency of the coating in the amounts employed.

In addition to the cross-linking agents previously mentioned there can be added for example to a partially, e.g., 85 percent converted hydrophylic polymer ethylene glycol dimethacrylate, ethylene glycol diacrylate, divinyl benzene, divinyl toluene, triallyl melamine, N,N-methylene-bis-acrylamide, glycerine trimethacrylate, diallyl maleate, divinyl ether, diallyl mono ethylene glycol citrate, allyl vinyl maleate, ethylene glycol vinyl allyl citrate, diallyl itaconate, ethylene glycol diester of itaconic acid, propylene glycol dimethacrylate, propylene glycol diacrylate, divinyl sulfone, hexahydro-l,3,5- triacryltriazine, triallyl phosphite, diallyl ester of benzene phosphonic acid, polyester of maleic anhydride with triethylene glycol, diethylene glycol diacrylate, polyallyl sucrose, polyallyl glucose, e.g., diallyl sucrose and triallyl glucose, sucrose diacrylate, glucose dimethacrylate, pentaerythritol diacrylate, sorbitol dimethacrylate.

The hydrophilic nonfogging polymer can even be formed into a self-sustaining film and laminated to the glass of other surfaces. Thus an already formed film could be placed on the glass and cured under heat and pressure to adhere to the glass. Alternatively, a layer of monomer containing a small amount of cross-linking agent, e.g., ethylene glycol monomethacrylate containing 0.5 percent of ethylene glycol dimethacrylate or itaconic acid could be placed on the glass surface, as an adhesive, the already formed nonfogging film applied on top and then the adhesive cured to laminate the glass to the nonfogging polymer.

As indicated the polymerization of the monomer as well as the subsequent curing is hastened by heat, e.g., to 90 C. Polymerization, however, can be carried out at widely varying temperatures, e.g., 20 0 150 C. or even up to 235 C.

Free radical catalysts such as t-butyl peroctoate, isopropyl percarbonate, benzoyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide can be employed to hasten polymerization and/or cure. The catalysts are usually employed in an amount of 0.05 to 1.0 grams, preferably 0.1 to 0.2 grams of catalyst per 100 grams of polymerizable material. The reaction is also catalyzed by ultraviolet light, gamma and other irradiation.

Polymerization can be carried out in the presence or absence of a solvent. Typical organic solvents include lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, glycol and glycol ethers, e.g., monomethyl ether of ethylene glycol, propylene glycol, ethylene glycol, diethylene glycol, dipropylene glycol, dimethyl formamide, tetrahydrofurane and the like.

, The polymeric material, preferably prior to cure and dissolved in an organic solvent (which can be diluted with chlorinated hydrocarbon, such as dichloroethylene or carbon tetrachloride or with'ketones such as methyl ethyl ketone, acetone) is applied to the surface of a transparent, nonporous substrate.

As indicated the polymeric mixture is preferably applied dissolved in solvent to a selected substrate such as glass. It can be applied by spraying, dipping, knife coating, roll coating, and brushing. The coating can then be allowed to dry by evaporation of the solvent into the atmosphere. Other methods for drying, such as infrared rays can also be used. The dry coating can then be cured at the same or more elevated temperatures, e.g., 90 to 235 C., preferably 100 to 150 C.

When a coating solution is employed the copolymer generally is between 5 and 15 percent by weight, preferably 8 to l 1 percent, although this can be widely varied. All of the coating materials described herein when applied to a transparent substrate produce a hard, scratch resistant, solvent resistant and abrasion resistant surface which is nonfogging and transparent. The cross-linked coatings have the hardest and most resistant properties.

If desired, the copolymer prepared according to the invention can be mixed with a polyepoxide containing at least two vicinal epoxy groups. Illustrative examples of such a polyepoxide include cycloaliphatic diepoxide such as vinyl cyclohexene dioxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (Unox 221); 3,4-epoxy-6methyl cyclohexylmethyl-3',4-epoxy-6-methylcyclohexane carboxylate (Unox 201); limonene dioxide, 3,4-epoxy cyclohexyl-'2',4'-dioxy- 6, 7-epoxy-spiroindane; britadiene diepoxide, Bisphenol A- epichlorhydrin. The ratio of polyepoxide to copolymer in the mixture can vary over a wide range. Thus I to 50 percent of the polyepoxide can be used based on the weight of the hydro philic nonfogging polymer.

There can also be added to any of the formulations minor amounts of conventional additives such as wetting agents, flow control agents, viscosity modifiers, cure accelerators, etc. The type and amount of such materials added to the mixture will be determined by the nature of the substrate to be treated.

Unless otherwise indicated'all parts and percentages are by weight.

The invention will be understood best in connection with the drawings wherein:

FIG. 1 is a view of an automobile windshield;

FIG. 2 is a sectional view along the line 22 of FIG. I;

FIG. 3 is a view of an eyeglass;

FIG. 4 is a sectional view along the line 4-4 of FIG. 3;

FIG. Sis a view ofa gun scope; and

FIG. 6 is a sectional view along the line 6-6 It will be realized in the drawings the thickness of the coating is greatly exaggerated.

Referring more specifically to FIG. 1 of the drawings, there is provided a conventional safety glass windshield 2 comprising two-pieces of glass 4 and 6 adhered together by a thin polyvinyl butyral layer 8 to make the windshield shatterproof. To the inner surface 10 of the windshield there is applied a 2 mil thick coating 12 of a cured Z-hydroxyethyl methacrylate itaconic acid copolymer (:5 No coating was applied to the outer surface 14 of the windshield. The resulting windshield was completely resistant to fogging under normal atmospheric conditions which cause fogging of Windshields. The coating was both light transmitting and optically clear.

The nonfogging coating as set forth supra was applied to the windshield surfaces as a spray 16 in ethyl alcohol from spray gun 17.

The solvent evaporated and the coating cured at about C.

Both sides of the Windshield can be sprayed with the coatmg.

As shown in FIGS; 3 and 4 eyeglasses designated generically at 20 having lens 22 were provided with a l mil light transmitting, optically clear coating 24 on the inner surface 26 of the lens of a hydroxyethyl acrylate-cinnamic acid-diethylene glycol diacrylate polymer (96.813202) and a similar coating 28 was applied to the outer surface 30 of the lens to produce a nonfogging eyeglass.

As disclosed in FIGS. 5 and 6 gunsight 32 having lens 34 was provided with a cured nonfogging, light transmitting optically clear coating 36 of a copolymer of 0.2-hydroxypropyl methacryIate-methacrylic acid (96:4) on the inner surface of the lens and a similar coating 38 on the outer surface of the lens to produce a nonfogging gunsight. Each coating was 1.5 mil thick.

EXAMPLE 1 EXAMPLE 2 Thirty grams of poIy-(Z-hydroxyethyl methacrylate) prepared in accordance with example 1 was dissolved in 70 ml. of methanol. To the solution was added 4.0 grams of peppermint oil. A glass plate for use as a vehicle windshield was coated with the methyl alcohol solution of the hydrophilic polymer. The resulting coating (0.005 inches thick, i.e., 5

. mils) was light-transmitting and optically clear, adherent and did not fog upon exposure to hot moist air.

A glass plate was similarly coated for use as a window to give a nonfogging window having the light-transmitting and optically clear, adherent coating. Similar nonfogging results were obtained when a mirror was coated with the methyl alcohol solution.

EXAMPLE 3 The procedure of example 2 was repeated but the pepper mint oil was omitted. The vehicle windshield had a 5 mil, lighttransmitting and optically clear coating of the hydrophilic polymer. The coated windshield did not fog upon exposure to hot moist air.

EXAMPLE 4 The procedure of example 2 was repeated but instead of the glass plate there was coated a plastic plate of methyl methacrylate for use as an aircraft windshield. The light-transmitting optically clear adherent coating obtained did not fog upon exposure to hot moist air. Similar results were obtained when the peppermint oil was omitted from the formulation.

EXAMPLE 5 The procedure of example 2 was followed to coat an optical element in the form of a camera lens having a reflectionreducing film of magnesium fluoride thereon to form a lighttransmitting, optically clear, reflection-reducing, nonfogging optical element.

Similar results were obtained when the peppermint oil was omitted from the formulation.

EXAMPLE 6 In a 1.5 liter reaction flask equipped with a timer, electric heater and a nitrogen inlet tube was charged 800 grams of ethylene glycol monomethyl ether, 180 grams of 2-hydroxyethyl methacrylate, 20 grams of acrylic acid and 2 grams of tbutyl peroctoate. The solution was heated and stirred under a carbon dioxide atmosphere at 85 C. for 6 hours. The polymer formed was precipitated by pouring the reaction solution into liters of rapidly agitated water. The precipitated polymer was isolated by filtration and dried. A yield of 185 grams was obtained.

One hundred grams of the polymer was dissolved in a mixture of 600 grams of ethylene glycol monomethyl ether and 300 grams of methyl ethyl ketone. To the solution was added 10 grams of a cycloaliphatic diepoxide (Unox 22l) and 0.05 gram of a flow control agent (Raybo 3). The Raybo 3 is not essential but its use makes a slightly smoother coating.

The solution was then sprayed on the interior surface of an automobile windshield to provide a wet film thickness of 10 mils. After drying the windshield was placed in a circulatory air oven at 250 F. for 2 hours tocure the polymer to the hard, scratch resistant condition. The windshield was nonfogging when subjected to moisture laden air.

EXAMPLE 7 One hundred grams of the polymer prepared in example 6 was dissolved in a mixture of 600 grams of ethylene glycol monomethyl ether and 300 grams of methyl ethyl ketone and the solution was then sprayed on the interior surface of a Ford automobile windshield to provide a wet film thickness of 10 mils. After drying the windshield was placed in a circulatory air oven at 250 F. for 4 hours to cure the polymer to the hard, scratch resistant condition. The windshield was nonfogging when subjected to moisture laden air.

EXAMPLE 8 Plastic eyeglass lenses produced by the polymerization of diethylene glycol bis(allyl carbonate) was coated with the coating solution of example 6 by a clipping process. After drying, the coating was cured for 1 hour at 275 F. to produce a hard, scratch resistant, nonfogging lens.

EXAMPLE 9 The procedure of example 8 was repeated except the Unox 221 and the Raybo 3 were omitted from the coating solution and the curing was done for 2 hours at 275 F. The lenses produced had a hard, scratch resistant nonfogging coating of the cured polymer on both sides thereof.

EXAMPLE 10 Eight hundred grams of ethylene glycol monomethyl ether, 180 grams of hydroxyethyl methacrylate, 20 grams of itaconic acid and 2 grams of t-butyl peroctoate were charged into a 1.5 liter reaction flask equipped with a stirrer, electric heating and a nitrogen inlet tube. The solution was heated and stirred under a nitrogen atmosphere at 85 C. for 6 hours. The polymer was precipitated by pouring the reactive solution into 10 liters of rapidly agitated water. The precipitated copolymer was isolated by filtration and dried. A yield of grams was obtained.

One hundred grams of the precipitated copolymer were dissolved in a solvent mixture comprising 600 grams of ethyl alcohol and 200 grams of Methyl Cellosolve. To the resulting solution there was added 10 grams of itaconic acid and I0 grams of 2-hydroxyethyl methacrylate along with 3 grams of Raybo 3 as a flow control agent and 0.5 grams of t-butyl peroctoate. 76.5 grams of ethyl alcohol was then added to dilute the mixture. The mixture was sprayed on the interior surface of an automobile windshield to a wet thickness of 10 mils. It was dried at room temperature and thereafter placed in a circulating air oven at 250 F. for 30 minutes. The result ing coating was scratch, solvent and abrasion resistant, was transparent and imparted a nonfogging character when the windshield was placed in an atmosphere: of high humidity.

EXAMPLE 1 l The procedure of example 10 was repeated except the Raybo 3 was omitted and both the interior and exterior surfaces of the windshield was sprayed. The resulting coatings were scratch, solvent and abrasion resistant, were transparent and imparted nonfogging properties to the windshield.

EXAMPLE 12 The procedure of example 10 was repeated except that 20 grams of cinnamic acid was employed in place of the itaconic acid in making the copolymer and 10 grams of cinnamic acid was employed in place of the itaconic acid added to the solution and no Raybo 3 was used. The inner surface of the windshield which received the coating was scratch, solvent and abrasion resistant and the windshield was nonfogging when tested in a Ford under an atmosphere of high humidity.

EXAMPLE l3 A solution was prepared from the following:

A copolymer of hydroxyethyl mcthacrylate and itaconic acid (94:6) parts Volan (methacrylate chromie chloride) l part hydroxyethyl methacrylate 1 part t-butyl peroctoate 0.01 part ltaconic acid menomethylcster 0.5 part Raybo 3 0.3 part Methyl Cellosolve 25 parts Ethanol 56.5 parts EXAMPLE 14 The procedure of example 13 was repeated omitting the Raybo 3. The copolymer coating obtained was then cured to produce a hard, scratch resistant green-tinted coating which had excellent adherence to the lens was obtained.

What is claimed is:

1. In combination an automobile having a coated, normally fogging transparent window the improvement comprising having as the coating on at least one surface thereof a nonfogging transparent, scratch resistant, solvent resistant, abrasion resistant, water-insoluble hydrophilic coating comprising a polymeric compound of the group consisting of hydrophilic acrylate and methacrylate polymers wherein the hydrophilic acrylate or methacrylate is selected from the group consisting of polymers of hydroxy lower alkyl acrylates, hydroxy lower alkoxy lower alkyl methacrylates, acrylamide, methacrylamide, diacetone acrylamide and methylolacrylamide.

2. A combination according to claim 1 wherein the window is a windshield.

3. A combination according to claim 1 wherein the polymer coating is selected from the group consisting of polymers of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate.

4. A combination according to claim 3 wherein the window is a glass window.

5. A combination according to claim 1 wherein the polymer includes 0.25 to 20 percent of a cross-linking agent.

6. A combination according to claim 5 wherein the window is a glass windshield. 

2. A combination according to claim 1 wherein the window is a windshield.
 3. A combination according to claim 1 wherein the polymer coating is selected from the group consisting of polymers of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate.
 4. A combination according to claim 3 wherein the windoW is a glass window.
 5. A combination according to claim 1 wherein the polymer includes 0.25 to 20 percent of a cross-linking agent.
 6. A combination according to claim 5 wherein the window is a glass windshield. 